(a) Field of the Invention
The present invention relates to a complex material prepared by bonding a nitride ceramic material to a metal material, and to a method of producing the complex material.
(b) Description of the Prior Art
The ceramic material, which exhibits various excellent properties, is widely used nowaday as construction materials, functional materials, etc. In many cases, the ceramic material is singly used as, for example, a construction material. However, to further widen the field of use of the ceramics, it is required that the ceramic material be capable of bonding to a metal material so as to form a complex material. Where the complex material is used as a construction material, a sufficiently high bonding strength is required in the joined portion. Where the complex material is used as a functional material, a continuity or the like is required at the boundary between the ceramic material and the metal material. However, the ceramic material and the metal widely differ from each other in the chemical properties such as the reactivity as well as in the physical properties such as the thermal expansion coefficient, making it difficult to achieve a metallurgical bonding of a high reliability between the ceramic and metal materials.
As a method of bonding ceramic and metal materials to obtain the complex material described above, U.S. Pat. No. 2,857,663 discloses a method which utilizes an active metal. This prior art utilizes the phenomenon that, if an active metal of, for exaple, Ti or Zr is alloyed with a transition metal such as Cu or Ni, the melting point of the resultant alloy is lowered by hundreds of degrees centrigrade. On the basis of this phenomenon, a metal material is bonded to an oxide ceramic material such as alumina, forsterite, beryllia or zirconia. In this case, however, the upper limit of the temperature under which the resultant complex material can be used is restricted by the melting point of the bonding material which is lower than the melting point of the metal material.
A method of forming a metal layer on the surface of ceramic materials (or metallizing method) is also known to the art as a method of composing a ceramic material to a metal material. This method makes it possible to impart the physical and chemical functions of the metal to the surface of the ceramic material. This method is also effective when used as a pretreatment in the operation of mechanically bonding a ceramic material to a metal material.
However, in the known metallizing method applied to a nitride ceramic material, the nitride ceramic material itself is low in its wettability with metal, with the result that the metallizing fails to proceed smoothly. It follows that, in spite of the complex metallizing process, the adhesive force of the resultant metal layer to the surface of the nitride ceramic material is very small. Particularly, in the case of a pure nitride ceramic material which does not contain a sintering assistant or the like, the adhesive force in question is negligibly small.